Stihl Chain Saw Question

I have a Stihl O21 chain saw about 5 years old, light usage. Last fall it
developed problems starting and it got so once I would get it running, it
would work until I shut it off then there was no getting it restarted until
it cooled. I took it to the repair shop and the guy said that the head was
warped and that it was not worth repairing. I talked to a different guy and
he told me that if I changed the gas/oil mix for 1 bottle of oil to a gallon
of gas, to 2 bottles of oil to a gallon of gas , I might get some use out of
it. I tried this, this weeked and the thing works like a champ. Starts every
time, hot or cold. My question now is, can this last or will it eventually
sieze up? Can someone explain to me what is going on, why the heavier oil
mix would make it run?
Thanks.

If the head was warped I dought you would have compression, how did he
check it, removing it is the only way. When a motor wont start hot see
if you are getting spark, bad hot coils or ignition modules can do that
until it cools. Or vapor lock from crap gas. I think your mechanics
head is warped.

I for one am glad you brought this to light and that I hope you don't listen
to that "kid on their parents computer" . I too am curious if anyone can add
to this. I once had a Poulan that acted exactly just like that.
Greyhound

Hey Brilliant One:
Perhaps the rings are shot and the additional oil helps increase the
compression, or perhaps you have a bad seal or gasket in the crankcase,
resulting in a leak.
Most chain saws don't have cylinder heads. They have one-piece cylinders
that bolt to the crankcase.
I'd say your mechanic is an idiot.
Either way, the saw is shot.

sorry to hear about this problem with your Stihl. Please share with
us...how did the head get warped? Is this something that can happen as
a result of running with no oil mixed in the gas? I ran my Dad's
outboard motor with no oil in the gas for about ten minutes...then the
piston actually flew out the side of the engine...
:-{
Bill

Ask any small engines mechanic: Chainsaws have one piece cylinders and
there is no such thing as a warped head on a chainsaw. The saw is not
shot, but it may need new parts. Usually if there is a hot start
related problem with the saw, the piston, which is soft aluminum, has
started to melt at the rings, causing small pieces of metal to flake
off, increasing friction, especially when the engine gets hot. At that
point. you can't get the thing to spin over fast enough to start.
A new piston, rings and cylinder gasket will cost about $100 just a
guess,and then you need to learn to put the thing together, but it is
worth doing on a $600+ saw. The cylinder has a steel sleeve, so it is
the piston which breaks down first. The cylinder walls will be scored,
but emery cloth and elbow grease can fix that good enough for a
firewood saw.
Running extra oil is not a long term solution, you're scoring the
cylinder, maybe beyond salvaging.
Too lean of a mix can cause the above melting of the piston, and the
saw will sometimes seize up in mid-stroke.
Sometimes if the damage is minimal, and it may be in this case, a bit
of piston polishing and a new ring will get you back to business for
less than $25. Find an old timer who knows how.
JohnK

I had a cheap Homelite that was supposed to be good for about 20 hours, but
I didn't get half that. My Stihl has a lot more hours and is still in top
shape. I'm sure the manufacturer knows, b ut they don't publish that
anyplace I've seen.

The only thing I can figure about the hot starting problem and the extra
oil"cure" is hat the rings are not sealing when it is hot and it is not
getting enough compression, and the added oil is helping them to seal. I
have heard of this years ago in older cars. Larry

Hot start problems are usualy Ignition module, Coil , Condenser, bad
plug wire, spark plug, vapor lock, air leak, or low hot compression or
simply flooding. Vapor lock caused by cheap gas vaporising in the carb
or line . Air getting into a cracked hose, loose bolt or screw, bad
primer , bad carb gasket leaning out the mixture. Most likely Ignition
or flooding. It could be Ignition Module-coil-consenser or simply bad
secondary ignition - Plug wire, Plug, a simple no spark when hot test
will show this.
My last failures were Ignition Module only when hot, second was plug
wire only when hot.
A compression test hot and cold will rule out head, cilinder-ring
issues and let you know true engine life.
A spark test hot will rule out ignition. If spark is not blue hot and
cold it is ignition.
It could be a bad plug, even new.
A wet plug and blue spark and good compression are flooding.
You have alot of simple things to check first, a warped head as your
mechanic said will not allow motor to run cold-no compression. Start
with better Regular gas only and check spark plug condition. Even plugs
are bought new bad, the stockboy or customer may have dropped it . Ive
bought them bad, and Ive dropped them in the store, and I put them back.

Log in

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.